The idea of transmitting energy wirelessly is more than a century old. At the end of the nineteenth century, the famous scientist Nikola Tesla researched ways to transmit large amounts of energy over long distances.
More recently, a number of solutions have been disclosed relating to the transmission of energy over shorter distances for consumer electronics applications.
U.S. Pat. No. 7,271,569 discloses a contactless inductive charger having a generally planar surface. An image, text or other visual indicator is disposed upon the substantially planar surface such that the visual indicator represents a preferred placement orientation for an electronic device for optimal inductive charging. The charger includes a primary coil positioned within the boundaries of the image, such that a user has a visual guide for placing the device on the charging surface for maximum efficiency in charging. The visual indicator, which may be a picture, outline, text or other directional indicator, may be geometrically similar to a shape of the electronic device or may be in the shape of a generic device.
Patent application US 2007/0279002 discloses a power source, a charging system, and an inductive receiver for mobile devices. A pad or similar base unit comprises a transmitter, which creates a magnetic field by applying an alternating current to a winding, coil, or any type of current carrying wire. A receiver comprises a means for receiving the energy from the alternating magnetic field and transferring it to a mobile or other device. The transmitter and/or the receiver may comprise a plurality of current carrying wires disposed adjacent to each other; different shapes and arrangements of the wires are considered.
Patent application US 2008/0067874 discloses a method and system for transferring power wirelessly to electronic devices. The system can utilize magnetic coupling between two coils at close proximity to transfer sufficient power to charge an electronic device. Embodiments pertain to an array of spiral coils that can be used to transmit power for transfer to receiver coils. Various embodiments can be referred to as PowerPad system. Embodiments can incorporate one or more of the following: planar inductors, PCB transformers, and very high frequency power supplies. Embodiments also pertain to planar inductors having characteristics that allow the production of even magnetic field, as well as systems that incorporate such planar inductors.
U.S. Pat. No. 5,596,567 discloses a battery charger and battery pack that are each provided with a wireless communications device to communicate over a wireless channel. The battery charger receives charging information from a memory housed in the battery pack, and commences a recharge process in accordance with the received information when the battery pack is electrically coupled to the charger.
U.S. Pat. No. 6,960,968 discloses a planar resonator for contactless power transfer using at least two electrically-isolated axis-aligned spiral-shaped conductors in a coupled inductor or transformer configuration. Signal or power transfer is then accomplished by coupling of magnetic flux. The coupling of electric flux is also accomplished. The first and second conductors have a predetermined self-resonant frequency. The resonator stores electric energy in an interface and at predetermined frequencies; the arrangement of the first and second conductors and the interface permits transfers of magnetic flux and electrical energy between the first and second conductors across the interface. The resonator facilitates contactless battery charging in devices such as cell phones and wearable electronics when the resonator can be woven into fabric or attached to a person's clothes.
The article by A. Karalis, J. D. Joannopoulos, M. Soljacic entitled “Efficient wireless non-radiative mid-range energy transfer” investigates whether, and to what extent, the physical phenomenon of long-lifetime resonant electromagnetic states with localized slowly-evanescent field patterns can be used to transfer energy efficiently over non-negligible distances, even in the presence of extraneous environmental objects.